A thin film transistor liquid crystal display (TFT-LCD) with the advantages of high picture quality, high space utilization rate, low power consumption, no radiation and the like, has become a mainstream product on the market. In the TFT liquid crystal display, at least one TFT is designed on each pixel, and each independent pixel on a screen is controlled through the TFT, so that the response time may be greatly improved.
Indium gallium zinc oxide (IGZO) is a new-generation material for a TFT active layer, and the carrier mobility of the IGZO is 5 to 10 times larger than that of amorphous silicon, so that the charge and discharge speed of pixel electrodes may be greatly improved, and the response speed of pixels may be improved to realize a faster refresh rate.
When the amorphous silicon is used as a material for the active layer, a metal electrode layer may be directly manufactured on the active layer, and then desired patterns of source and drain electrodes are formed through etching; and when the IGZO is used for the active layer, since the IGZO is not anticorrosive like the amorphous silicon and an IGZO layer is easily damaged in the etching process of the source and drain electrodes, an etch stop layer needs to be manufactured on the IGZO active layer first to protect the IGZO layer, and then a source and drain metal electrode layer is manufactured. FIG. 1 is a schematic top view of a thin film transistor in the prior art. As shown in FIG. 1, the thin film transistor comprises a source electrode 1, a drain electrode 2, a gate electrode 3, an IGZO active layer (not shown in the figure), an etch stop layer 5 on the IGZO active layer and two opposite via holes formed in the etch stop layer 5, wherein the source electrode 1 is electrically connected with the IGZO active layer through the via hole 7, and the drain electrode 2 is electrically connected with the IGZO active layer through the via hole 6. In the practical TFT manufacturing process, due to the influence of minimum precision (namely resolution) of an exposure machine, the patterns close to the minimum precision are influenced by imaging, development and etching, then the formed via holes have certain deformation, the practically formed via holes are of rectangles with rounded corners and even are approximately round. The source electrode and the drain electrode are connected with the active layer through the via holes, and the width of a channel formed when the TFT is turned on is determined by the diameters of the round holes. Thus, the channel length of the TFT is determined by the distance between the via hole 6 and the via hole 7, and the width of the channel of the TFT is determined by the side lengths (diameters) of the via hole 6 and the via hole 7.
The prior art has the following problems: in the structure as shown in FIG. 1, the parasitic capacitance between the source electrode and the gate electrode of the TFT and the parasitic capacitance between the drain electrode and the gate electrode of the TFT are relatively high, so that when the TFT is used for a liquid crystal display, fluctuation of a pixel voltage is increased, and the display effect is reduced.